1. Field of the Invention
The present invention relates to end effectors used in robotics and other applications. More particularly, the present application relates to reconfigurable end effectors.
2. Description of the Prior Art and Related Information
End effectors, sometimes referred to as mechanical hands or robotic hands, are employed for a wide range of applications where mechanical manipulation is required. In particular, virtually any industrial or other application of robotics requires an end effector of some type to provide a manipulation capability. Accordingly, a wide variety of different types of end effectors are known in the art and a great deal of effort has gone into their design and development.
Prior art end effectors may be broadly grouped into two types: end effectors designed for specific applications, typically industrial applications, and application non-specific end effectors which are reconfigurable to adapt to various tasks.
Application specific end effectors are widely employed in industry in various applications such as welding, assembly, holding objects for drilling and punching, etc. Application specific end effector designs typically have relatively few degrees of freedom and limited reconfigurability. Specific designs of such application specific end effectors include curved end effectors for encircling or clamping round or cylindrical objects, multiple pronged end effectors for providing a concentric grip on curved objects, end effectors for providing a plier type grip for grasping objects, platform-like end effectors for providing a cradling or lifting force and many other specific configurations employed for specific applications. A wide variety of such application specific end effectors are illustrated in Mechanical Hands Illustrated, Ichiro Kato, ed. (Survey Japan 1982). Typical actuation mechanisms for such application specific end effectors include hydraulic and worm gear type mechanisms due to their simplicity and strength. The principal advantages of application specific end effectors are high strength, relatively simple control algorithms, relatively simple mechanical structures with a limited number of moving parts, and durability. Such end effectors are limited in their reconfigurability, however, and need to be specially designed for each application.
Application non-specific end effectors typically have designs directed to providing a high degree of reconfigurability and manipulation capability rather than strength or durability. As a result, such end effector designs are usually complex, having a large number of degrees of freedom and complex actuation mechanisms. Frequently application non-specific end effectors attempt to emulate the human hand and therefore application non-specific end effectors are often referred to as robotic hands. The most widely known and highly regarded robotic hands employ three to four digits, each digit having two or three degrees of freedom. The motion of the individual digits is typically controlled by tendons coupled to actuators displaced from the robotic hand itself.
One such robotic hand is the Utah-MIT dextrous hand which has been described, for example, in Machine Design (June 26, 1986), p. 40. The Utah-MIT dexterous hand has four digits, three fingers and a "thumb" (i.e., an opposable digit), each digit activated by a series of tendons routed over pulleys. The tendons are in turn connected to pneumatic actuators displaced from the hand. The Utah-MIT dexterous hand also has a "wrist" degree of freedom with associated tendons, pulleys and actuators. In combination the hand and wrist employ 184 pulleys for guiding the tendons.
Another example of a highly reconfigurable robotic hand is the so-called Salisbury hand. The Salisbury hand is shown, for example, in Robots, Philip de Ste. Croix, ed. (Salamander Books 1985), p. 53. The Salisbury hand has three digits each having three joints. The digits of the Salisbury hand are also tendon controlled providing independent control of all nine joints in the hand. A complex mathematical control algorithm in combination with the nine degrees of freedom of the hand results in a highly manipulative hand.
Another highly reconfigurable hand is manufactured by Victory Enterprises Technology, Inc. of Austin, Tex. The Victory Enterprises Robotic Hand has four digits, one of which is opposable in a manner emulating the human hand in general design. The Victory Enterprises hand is also tendon controlled with the tendons coupled to linear lead screw type actuators.
The above-described tendon controlled robotic hands, while having a high degree of adaptability for various grasping and holding applications, suffer from a lack of strength suitable for many industrial or other heavy applications. Such tendon actuated robotic hands often do not have significantly more grasping or holding power than a human hand. Also, the large numbers of pulleys and tendons used to independently control the various joints of the digits require complex mechanical designs with many moving parts. Such complexity and large numbers of moving parts adds to the cost of the robotic hand and also increases the possibility of failure of the hand. The complexity also requires complex control algorithms which add to the cost and complexity of the overall system. As a result, highly reconfigurable robotic hands are at present relegated to a research role and are not suitable for industrial or other commercial applications.
Therefore, a need presently exists for a robotic hand having high strength, durability, and a relatively simple mechanical structure not requiring complex control algorithms, while having a high degree of reconfigurability and adaptability for different tasks.